Patent GB-1416273-A (GB)
Title: Recovery of paper fibre from municipal refuse
IPC: B03B9/06
Filed: 1973-02-09
Abstract: 1416273 Wet separating BLACK CLAWSON FIBRECLAIM INC 9 Feb 1973 [9 Feb 1972] 6582/73 Heading B2H [Also in Divisions Dl and D2] In the recovery of papermaking fibres from refuse, these fibres are required to be separated from "light contaminant materials" i.e. organic materials which have specific gravities similar to that of the fibres or which have higher specific gravities but behave hydrodynamically as if their specific gravities were less than their real value and the maximum particle size of which does not exceed the size of the largest paper fibre. Examples of such contaminants are animal, vegetable or mineral grease or wax, vegetable and meat particles, hair, synthetic fibres, vegetation residue such as grass clippings and fragments of leaves. The separation is achieved by (a) forming from the refuse an aqueous slurry the solid constituents of which are mainly the contaminated paper fibres (b) pumping the slurry into a centrifugal flotation unit (comprising a truncated conical vessel having its base uppermost and its apex directed downwardly) through an inlet port adjacent its base (c) maintaining the supply to the inlet port sufficiently high to develop in the vessel centrifugal force conditions to cause vertical separation of the slurry into an outer fraction containing the majority of the paper fibres and an inner fraction containing the majority of the light contaminate materials and (d) maintaining the discharge flow through outlet ports (one each in the vessel base and apex) in a predetermined relation such that the two fractions are discharged separately through the outlet ports, Step (b) may be preceded by a refining treatment to loosen grease from the paper fibres and/or a treatment wherein dissolved air is mixed in the slurry. In the system represented by Fig. 1, solid waste materials are fed by a conveyor 12 into a treatment tub 10 whence relatively infrangible materials are extracted by a junk remover 13 through which an aqueous medium such as water is fed into tub 10 from a line 14. A rotor 15 subjects the waste to violent hydraulic and mechanical shear forces to reduce the frangible content to predetermined particle size for extraction through a perforated bed plate 16. A slurry containing the reduced particles is pumped at 19 through line 18 to centrifugal cleaner 20 through the apex of which most of the gritty inorganics are removed at 22. The remainder of the slurry passes through line 24 into coarse screening apparatus 25 accepts from which pass through line 27 to a fine screen 30 thence by pump 31 to a centrifugal cleaner 33. Accepted stock from the latter passes through a pump 39 to another centrifugal cleaner 40 accepts from which are delivered by a line 41 to an inclined screen fines remover 42. Rejects pass, as through lines 26, 34, 36, 43 to a disposal line 35. The accepted stock from remover 42, containing solids consisting of the paper fibre and light contaminant materials, is delivered by pump 44 through line 45 to a centrifugal flotation unit 50 provided with inlet port 51 and outlet ports 52 and 53 through which, as a result of conditions obtained by proportioning the ports and controlling the feed and pressure, the outer (accepts) and inner (rejects) fractions are discharged and may pass through a line 57 to stations 60, 61, 62, representing an additional supply pump and cleaner, a digester and a final stage of washing and dewatering apparatus, and to a pyrolysis or hydrogenation station 70. In specific modifications, one or both screens 25 and 30 is/are replaced by a centrifugal flotation unit in order to eliminate particles which tend to behave hydrodynamically like paper fibres; a further treatment stattion (65) is provided between fines remover 42 and flotation unit 50, Fig. 2 (not shown); air is injected into the slurry ahead of unit 50, Fig. 3 (not shown).